Apparatus and method for in situ production of fuel for a fuel cell

ABSTRACT

Fuel cell fuel supplies having single and multiple compartments for storing and containing fuel cell fuel precursor reagents. These fuel supplies allow storage and packaging of precursors for in situ production and use of fuel cell fuel. A method for making fuel cell fuel and a fuel cell system is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application claiming priority to U.S.patent application Ser. No. 10/854,540 filed on May 26, 2004 now U.S.Pat. No. 7,329,470. The parent case is incorporated by reference hereinin its entirety.

FIELD OF THE INVENTION

This invention generally relates to an apparatus and method forproducing fuel. This invention more particularly relates to a fuelsystem and method for the production of fuel for use in a fuel cell.

BACKGROUND OF THE INVENTION

Fuel cells are devices that directly convert chemical energy ofreactants, i.e., fuel and oxidant, into direct current (DC) electricity.For an increasing number of applications, fuel cells are more efficientthan conventional power generation, such as combustion of fossil fueland more efficient than portable power storage, such as lithium-ionbatteries.

In general, fuel cell technologies include a variety of different fuelcells, such as alkali fuel cells, polymer electrolyte fuel cells,phosphoric acid fuel cells, molten carbonate fuel cells, solid oxidefuel cells and enzyme fuel cells. Some fuel cells utilize compressedhydrogen (H₂) as fuel. Compressed hydrogen is generally kept under highpressure, and is therefore difficult to handle. Furthermore, largestorage tanks are typically required and cannot be made sufficientlysmall for consumer electronic devices. Proton exchange membrane (PEM)fuel cells use methanol (CH₃OH), sodium borohydride (NaBH₄),hydrocarbons (such as butane) or other fuels reformed into hydrogenfuel. Conventional reformat fuel cells require reformers and othervaporization and auxiliary systems to convert fuel to hydrogen to reactwith oxidant in the fuel cell. Recent advances make reformer or reformatfuel cells promising for consumer electronic devices. Other PEM fuelcells use methanol (CH₃OH) fuel directly (“direct methanol fuel cells”or DMFC). DMFC, where methanol is reacted directly with oxidant in thefuel cell, is the simplest and potentially smallest fuel cell, and alsohas promising power application for consumer electronic devices. Solidoxide fuel cells (SOFC) convert hydrocarbon fuels, such as butane, athigh heat to produce electricity. SOFC requires relatively hightemperature over 800° C. for the fuel cell reaction to occur.

The chemical reactions that produce electricity are different for eachtype of fuel cell. For DMFC, the chemical-electrical reaction at eachelectrode and the overall reaction for a direct methanol fuel cell aredescribed as follows:

Half-reaction at the anode:CH₃OH+H₂O→CO₂+6H⁺+6e ⁻

Half-reaction at the cathode:1.5O₂+6H⁺+6e ⁻→3H₂O

The overall fuel cell reaction:CH₃OH+1.5O₂→CO₂+2H₂O

Due to the migration of the hydrogen ions (H⁺) through the PEM from theanode to the cathode and due to the inability of the free electrons (e⁻)to pass through the PEM, the electrons must flow through an externalcircuit, thereby producing an electrical current through the externalcircuit. The external circuit may be used to power many useful consumerelectronic devices, such as mobile or cell phones, calculators, personaldigital assistants, laptop computers, and power tools, among others.

DMFC is discussed in U.S. Pat. Nos. 5,992,008 and 5,945,231, which areincorporated by reference in their entireties. Generally, the PEM ismade from a polymer, such as Nafion® available from DuPont, which is aperfluorinated material having a thickness in the range of about 0.05 mmabout 0.50 mm, or other suitable membranes. The anode is typically madefrom a Teflonized carbon paper support with a thin layer of catalyst,such as platinum-ruthenium, deposited thereon. The cathode is typicallya gas diffusion electrode in which platinum particles are bonded to oneside of the membrane.

Another fuel cell reaction for a sodium borohydride reformer fuel cellis as follows:NaBH₄(aqueous)+2H₂O→(heat or catalyst)→4(H₂)+(NaBO₂)(aqueous)

Half-reaction at the anode:H₂→2H⁺+2e ⁻

Half-reaction at the cathode:2(2H⁺+2e ³¹)+O₂→2H₂OSuitable catalysts for this reaction include platinum and ruthenium, andother metals. The hydrogen fuel produced from reforming sodiumborohydride is reacted in the fuel cell with an oxidant, such as O₂, tocreate electricity (or a flow of electrons) and water byproduct. Sodiumborate (NaBO₂) byproduct is also produced by the reforming process. Asodium borohydride fuel cell is discussed in United States publishedpatent application no. 2003/0082427, which is incorporated herein byreference.

One of the more important features for fuel cell application is fuelstorage. The fuel supply should also be easily inserted into the fuelcell or the electronic device that the fuel cell powers. Additionally,the fuel supply should also be easily replaceable or refillable.

United States published patent publication no. 2003/0082427 discloses afuel cartridge where sodium borohydride fuel is reformed within thecartridge to form hydrogen and byproduct. However, the prior art doesnot disclose a fuel supply that allows in situ production of fuel orthat contains reagents amenable to non-corrosive, low cost storage, orfuel supplies with the advantages and features described below.

SUMMARY OF THE INVENTION

Hence, the present invention is directed to a fuel supply that allows insitu production of fuel for a fuel cell.

The present invention is also directed to a fuel supply that containsprecursor reagents that can react to form fuel for a fuel cell.

One aspect of the present invention is directed to a fuel supplyallowing in situ production of fuel for a fuel cell. This fuel supplyhas a first compartment that contains a first precursor reagent. Thesystem also includes a second compartment that contains a secondprecursor reagent such that the contents of the first container and thesecond container are mixable to create a fuel that powers the fuel cell.

Another aspect of the invention is directed to a method for producingfuel for a fuel cell that comprises the step of providing a fuel cellfuel supply having a first compartment that contains a first precursorreagent. It also comprises the step of causing the first precursorreagent to react with a second precursor reagent to form the fuel. Thereaction can occur within the fuel supply or outside of the fuel supply.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which form a part of the specification andare to be read in conjunction therewith and in which like referencenumerals are used to indicate like parts in the various views:

FIG. 1 is a cross-sectional view of a fuel cartridge in accordance withone embodiment of the present invention having multiple precursorreagent compartments;

FIG. 2 is a cross-sectional view of another fuel cartridge in accordancewith another embodiment of the present invention having a singleprecursor reagent compartment;

FIG. 3 is a schematic view of another fuel cartridge having top andbottom compartments in accordance with another embodiment of the presentinvention wherein fuel precursor reagents mix outside of the cartridge;and

FIGS. 4 and 4A are schematic views of other fuel cartridges havingside-by-side compartments in accordance with another embodiment of thepresent invention wherein fuel precursor reagents mix outside of thecartridge.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in the accompanying drawings and discussed in detailbelow, one aspect of the present invention is directed to a fuel supplythat contains one or more precursors to a fuel for a fuel cell. Suchfuel includes, for example methanol/water mixtures of varyingconcentrations, borohydrides, borane, and hydrazine. Suitableprecursor(s) include, for example, water, dimethyl dicarbonate,borane-containing polymers, sodium carbonate, azine, hydrogen peroxide,ammonia, and methylethyl ketone.

Another aspect of the present invention is directed to a method formaking fuel for a fuel cell. This method includes the step of combiningone or more precursor reagents from a fuel supply with one (or more)other precursor reagent(s) from inside or outside of the same fuelsupply. The reaction between the precursor reagent(s) can occur insideor outside of the fuel supply.

Another aspect of the present invention is similarly directed to a fuelsystem containing one or more precursors to a fuel for a fuel cell.

The present invention further covers precursors in addition to theabove-mentioned precursors for any type of fuel cell fuels, as describedbelow. Such additional fuels include, but are not limited to, ethanol orother alcohols, chemicals that can be reformatted into hydrogen, orother chemicals that may improve the performance or efficiency of fuelcells. Fuels suitable for use in this invention therefore also include amixture of methanol, hydrogen peroxide and sulfuric acid, which flowspast a catalyst formed on silicon chips to create a fuel cell reaction.Suitable fuels further include hydrocarbon fuels as well, which include,but are not limited to, butane, kerosene, alcohol and natural gas,disclosed in United States published patent application no.2003/0096150, entitled “Liquid Hereto-Interface Fuel Cell Device,”published on May 22, 2003, which is incorporated herein by reference inits entirety. Suitable fuels also include liquid oxidants that reactwith fuels. The present invention is, therefore, not limited to any typeof fuels, electrolytic solutions, oxidant solutions, liquids, or solidscontained in the fuel supply or otherwise used by the fuel cell system.The term “fuel” as used herein includes all fuels that can be reacted infuel cells, and includes, but is not limited to, all of the abovesuitable fuels, electrolytic solutions, oxidant solutions, liquids,solids, and/or chemicals and mixtures thereof.

Fuel cells according to this invention therefore may include potassiumhydroxide (KOH) electrolyte, which is usable with metal fuel cells oralkali fuel cells, and can be stored in fuel cartridges. For metal fuelcells, fuel is in the form of fluid borne zinc particles immersed in aKOH electrolytic reaction solution, and the anodes within the cellcavities are particulate anodes formed of the zinc particles. KOH fuelis disclosed in United States published patent application no.2003/0077493, entitled “Method of Using Fuel Cell System Configured toProvide Power to One or More Loads,” published on Apr. 24, 2003, whichis incorporated herein by reference in its entirety.

As used herein, the term “fuel supply” includes, but is not limited to,disposable cartridges, refillable/reusable cartridges, cartridges thatreside inside the electronic device, cartridges that are outside of theelectronic device, fuel tanks, fuel reservoirs, fuel refilling tanks,other containers that store fuel and the tubings connected to the fueltanks, containers, the fuel cell or the electronic device that the fuelcell powers. While a cartridge is described below in conjunction withthe exemplary embodiments of the present invention, it is noted thatthese embodiments are also applicable to other fuel supplies and thepresent invention is not limited to any particular type of fuelsupplies.

FIG. 1 illustrates cartridge 10 for storing fuel precursors to reformatfuels, such as those to produce sodium borohydride, methanol, ammoniaborane, or hydrazine. After the precursors react to produce fuel, thefuel can be used directly in the fuel cell, or be reformatted to formhydrogen. The hydrogen is then transported to a fuel cell, e.g., a PEM,to be converted into electricity and byproducts. It is understood thatany fuel that can be reformed to produce hydrogen is usable with thiscartridge and is therefore within the scope of this invention.

The embodiment described herein, described below are similar to thosefully discussed in co-pending patent application Ser. No. 10/679,756,entitled “Fuel Cartridges and Methods for Making Same” filed on Oct. 6,2003, and co-pending patent application Ser. No. 10/629,004, entitled“Fuel Cartridge with Flexible Liner” filed on Jul. 29, 2003,respectively. These commonly owned applications are incorporated hereinby reference in their entireties.

Cartridge 10 contains chamber 12, which is divided into firstcompartment 14 and reactant compartment 16. The compartments areseparated by movable wall 18, which has wiper 20. Wiper 20 or anelastomeric O-ring forms a seal with the inside surface of chamber 12,so that first compartment 14 is not in fluid communication withcompartment 16. A movable membrane, an extensible membrane or the likecan replace movable wall 18, so long as the volume of reactantcompartment 16 increases while the volume of first compartment 14decreases. Alternatively, the seal formed by wiper 20 or the O-ring canbe omitted if first compartment 14 and reactant compartment 16 containinner liners to store fuel precursors and reactant, separately. Suchliners are fully disclosed in the commonly owned, co-pending '004 patentapplication.

First compartment 14 encases a third compartment 15. Fuel precursorreagents stored in compartments 14 and 15 are mixed to produce fuel.Storing fuel in the form of precursor reagents can increase storage orshelf life of the fuel cartridge, when the reagents are less corrosivethan the fuel. Third compartment 15 is breakable and contains a firstfuel precursor reagent. A second precursor reagent inside of compartment14 surrounds third compartment 15. When fuel is needed, e.g., before thecartridge is attached to a fuel cell, the walls of chamber 12 can bedepressed thereby breaking compartment 15 releasing the first precursorreagent into the second precursor reagent. These precursor reagents mixinside the fuel cartridge to form a reformat fuel. An optional catalystcan be provided to facilitate the reaction. The reformat fuel is thentransported to reaction chamber 22 to react in the presence of anothercatalyst or to be heated. Suitable catalysts for the production ofhydrogen include platinum or ruthenium or other metals.

Alternatively, compartment 14 provides a mixture of fuel precursorreagents that are un-reacted or only partially-reacted. In alternateembodiments, the precursor reagents do not form a fuel until heated orotherwise acted upon outside of compartments 14 and 15. Thus, as asimple precursor mixture, the precursors can be heated and/or exposed toa catalyst in reaction chamber 22 to form the reformatted fuel.Precursor reagents in such alternate embodiments may also contain or beexposed to heat or catalysts at any stage outside of compartments 14 and15 to promote the production of fuel.

Fuel and un-reacted precursor(s) can be transported by pump 24.Alternatively, the fuel and un-reacted precursor(s) can be transportedthrough a wicking or capillary medium. Alternatively, fuel andun-reacted precursor(s) can be transported by pressure resulting fromthe build-up of gaseous byproduct from the precursor reagent reaction,the creation of hydrogen, or any other reaction. Transportation of fuelcell fuels by wicking or capillary action is fully disclosed inco-pending patent application Ser. No. 10/356,793, entitled “FuelCartridge for Fuel Cells,” filed on Jan. 31, 2003. This application isincorporated herein by reference in its entirety. An optional checkvalve 26, i.e., one-direction flow valve, can be positioned betweenreaction chamber 22 and fuel precursor compartment 14.

In an alternate embodiment, the production of reformat fuel requiresadditional materials not stored in compartments 14 and 15. Thus aseparate compartment (not shown) may store a third precursor reagent, acatalyst, a heat mixture, or surplus amounts of one of the precursorreagents or solvents found in compartments 14 and 15. These addedreagents are separately transported to reaction chamber 22 by any of theabove-described methods for transporting fuel and un-reacted precursors.

Reactant hydrogen gas (H₂) and liquid byproducts produced in reactionchamber 22 are then transported in channel 30 to reactant compartment 16of chamber 12. Reactant compartment 16 has membrane 32, which allowshydrogen gas to pass through to internal spacing 34 inside cartridge 10.Consequently, aqueous byproducts are retained inside reactantcompartment 16. As shown by the dash lines, hydrogen gas can beselectively transported out of cartridge 10 through control valve 36 tothe fuel cell to produce electricity. Control valve 36 is fullydisclosed in commonly owned, co-pending patent application Ser. No.10/629,006, entitled “Fuel Cartridge with Connecting Valve,” filed onJul. 29, 2003. The disclosure of this application is incorporated hereinby reference in its entirety. Membrane 32 is selected so that a certainpressure differential across the membrane is necessary for hydrogen gasto migrate across the membrane. Due to the presence of hydrogen gas, thepressure in reactant compartment 16 is higher than the pressure in fuelcompartment 14 and movable wall 18 is pushed by this differentialpressure to force fuel out of fuel compartment 14 to reaction chamber22. To ensure that pressure inside reactant compartment 16 remainshigher than fuel compartment 14, a poppet valve as described in the '004application can be used in conjunction with membrane 32. Alternatively,in place of a poppet valve, a porous member, such as a filler, a foam orthe like, can be used. Such porous member requires a pressure dropacross it for hydrogen to move from reactant compartment 16 to internalspacing 34 and valve 36.

In this embodiment, when hydrogen fuel is no longer needed, valve 36 isshut off. Hydrogen in internal spacing 34 stops flowing out and thiscreates a back pressure. This back pressure stops the flow into reactantchamber 16, which also stops the flow in the fluid circuit. This stopsthe reaction and fuel production. When fuel is needed again, valve 36 isopened and pressurized hydrogen gas flows out of the cartridge, and thisdrops the pressure in internal spacing 34, which allows hydrogen gas toflow from reactant chamber 16 to internal spacing 34. This flow againpulls fuel from fuel compartment 14 to reaction chamber 22 to re-startthe reaction. Pump 24 can be used to meter the flow of fuel fromcompartment 14 by knowing the flow rate(s) through the pump and the timethat the pump is on. Cartridge 10 may also have relief valve 33, such asa poppet valve, which is configured to open when the pressure ininternal spacing reaches a predetermined level.

Referring again to FIG. 1, cartridge 10 may further contain at least onebreakable fourth compartment 17, containing a precursor that can be thesame or different from the precursor in third compartment 15. In oneembodiment, where compartments 15 and 17 contain the same precursor,fuel is first produced (as more generally described above) by reactingthe precursor reagent from compartment 15 with an excess amount of theprecursor that surrounds compartment 15. Fourth compartment 17, which isbreakably secured to the inside wall of compartment 14, releasesadditional precursor reagent when it is subsequently broken off. This isaccomplished as byproduct gas contents in compartment 16 increase andpush movable wall 18 further into compartment 14. As a result, breakingmember 41 disposed on wall 18 moves toward and breaks compartment 17 torelease or create additional precursor reagent therefrom. Mixing withthe remaining precursor within compartment 14, the released precursorreagent from compartment 17 creates a fresh supply of fuel. Used in thisfashion, a series or an array of breakable or pierceable compartmentssuch as compartment(s) 17 may be employed to provide a continual andextended supply of fuel. Compartments 17 can also be used in place ofcompartment 15. Alternatively, compartment(s) 17 are detachable and areconnected to the walls of compartment 14 by a tearable or weakenedsection, so that when movable wall 18 contacts a detachable compartment17, detachable compartment 17 is detached preferably along the weakenedsection to release the precursor reagent contained herein. The weakenedsection can be a section with less thickness, which can be a tear strip.

Suitable materials for compartments 15 and 17 include glass (forbreakable compartments), and natural rubber (for breakawaycompartments), polyethylene (including low density to high density PE),ethylene propylene (EP), EPDM and other thin polymeric films (forpiercable compartments). In one embodiment, the polyethylene in suchpierced chambers is fluorinated and is substantially free of metal ionsto ensure low permeation. The polyethylene can be laminated with a vaporbarrier layer, such as aluminum foil or fluorine treated plastics, toreduce, for example, methanol permeation.

In the embodiment shown in FIG. 1, when the produced fuel can be useddirectly by the fuel cell, e.g., methanol fuel and DMFC, reactionchamber 22 and reactant compartment 16 and related components can beomitted. In other words, fuel cartridge may simply comprise firstcomponent 14, containing a first precursor reagent and third compartment15 containing a second precursor reagent. Third component 15 isbreakable so that the reagents are mixed before the cartridge isconnected to a fuel cell.

Another embodiment of a fuel supply in accordance with the presentinvention, which has a single precursor reagent compartment, is shown inFIG. 2. Cartridge 100 has a chamber 120, which holds liner 140. Liner140 holds a first fuel precursor reagent that can be delivered to anexternal reaction chamber to mix with other precursor reagent(s) throughvalve 160. Valve 160 can be provided to control the transport ofprecursor reagent out of liner 140. Valve 160 can have any construction.Preferably, valve 160 is substantially similar to valve 36, discussedabove. Alternatively, a second precursor reagent can be introduced intoliner 140 through valve 160 to create fuel within the cartridge beforethe cartridge is connected to a fuel cell.

In accordance with another aspect of the invention, the cartridge maycomprise two or more compartments. As shown in FIG. 3, fuel cartridge210 may have compartments 246 and 248, where one compartment is locatedon top of the other compartment. Preferably, one contains a firstprecursor and the other contains a second precursor. A filler insert isincluded in each compartment to transport the precursors out of thecartridge by capillary action. In the embodiment shown in FIG. 3, theconnecting column 250 of compartment 248 is disposed concentricallyinside connecting column 252 of compartment 246. Preferably, column 250is isolated from column 252 by a liquid proof film. As shown, eachcolumn is connected to capillary disks to ensure that the liquidcontained therein is wicked out of the compartments. Alternatively, thecompartments can be positioned side-by-side, such as compartments 254and 256 illustrated in FIG. 4 and the compartments can have liners tostore fuel, as illustrated in FIG. 4A. Each compartment 254, 256contains a filler insert comprising a connecting column 258, 260,respectively, and capillary disks to wick the liquids out of thecompartments. The cartridges in FIGS. 3 and 4 are disclosed in theco-pending '793 patent application previously incorporated herein byreference. In these embodiments, the two precursor streams are pumpedinto external mixing chamber 262. These embodiments are suitable fornon-reformat fuel or fuels that can be pumped directly into the fuelcell, e.g., methanol. When pumps are used, the filler or wickingmaterials may be omitted.

Pumps useful for this invention are described in the commonly owned,co-pending '756 application previously incorporated herein by reference.A suitable pump is a micro-electro-mechanical-system (MEMS)piezoelectric pump. The precursor reagents combine either at the fuelcell or at any location upstream from it. Thus, in a preferredembodiment, two reagents combine prior to flow into the fuel cell asdiscussed in FIGS. 3 and 4.

It is noted that the present invention may use any number ofcompartments to contain any type of precursor reagent or precursorreagent mixture. For example, the fuel cartridge may have multiple innerliners. In another example, the fuel cartridge may have a first innerliner or other internal compartment for a solid precursor reagent and asecond inner liner or other internal compartment for an appropriatecomplimentary liquid precursor reagent.

Illustrative examples of several fuel cell fuel precursor reagentssuitable for use in accordance with the present invention include thefollowing examples:

Example 1 In Situ Production of Borohydrides

One aspect of the present invention allows for in situ formation ofborohydrides (including various salts such as, but not limited to,ammonium borohydride, calcium diborohydride, and sodium borohydride)according to several known processes for producing various borohydrides.

As mentioned above, sodium borohydride is a reformat fuel cell fuel thatreacts to produce hydrogen according to the following chemical formula:NaBH_(4(aq))+2H₂O→(heat or catalyst)→4(H₂)+NaBO_(2(aq))

The present invention accordingly provides for in situ production ofsodium borohydride (and other borohydrides) so that it can be used insuch a reaction to produce hydrogen. Several processes describing theproduction of borohydrides are generally set forth in U.S. Pat. Nos.6,433,129 and 6,586,563, which are incorporated herein by reference intheir entireties. For example, according to the '563 patent sodiumcarbonate can be reacted with diborane to produce sodium borohydride:2Na₂CO₃+2B₂H₆→3NaBH₄+NaBO₂+2CO₂Hence, diborane and aqueous solutions of sodium carbonate can be thefirst and second precursor reagents to produce a borohydride.

More generally, the '563 patent also teaches, among other things, aprocess for producing borohydride compounds that includes the reactionof a carbonate of the formula Y₂CO₃ in aqueous solution at a temperatureof about −5° to about 20° C. with diborane to produce the borohydrideYBH₄, where Y is a monovalent cationic moiety. Thus, several potentialprecursor reagent combinations for ambient and cold formation ofborohydride salts are known.

Diborane can be stored and used as a precursor reagent for the presentinvention in polymer form. U.S. Pat. No. 3,928,293, which isincorporated herein by reference in its entirety, discloses solidcrosslinked thiohydrocarbon borane hydride polymers and their use asreducing agents for aldehydes, ketones, lactones, oxides, esters,carboxylic acids, nitrites and olefins. These borane polymers, althoughstable at room temperature, can release borane (BH₃) under conditions ofreduced pressure or heat and are disclosed as being useful as aconvenient means of storing borane. Other polymers useful as precursorreagents for the production of borane are taught in U.S. Pat. Nos.3,609,191 and 4,410,665, which are both incorporated herein by referencein their entireties.

These borane polymer complexes are less reactive as diborane, but will,with increased temperature or reaction time, enter into essentially thesame reactions as diborane. Because they are water soluble, when mixedwith aqueous sodium carbonate they will produce sodium borohydrideaccording to the following chemical equation:(—[CH₂—S—CH₂]—.BH₃)₄+2Na₂CO_(3(aq))→3NaBH₄+NaBO₂+2CO₂+(—[CH₂—S—CH₂]—)₄As seen, a thiohydrocarbon polymer associated with borane reacts withaqueous sodium carbonate to produce sodium borohydride. Thus, polymerssuch as the ones described in the '293 patent, when stored in tandemwith sodium carbonate as two fuel precursor reagents, are suitable forstorage and use in the fuel supplies of the present invention.

Alternatively, other precursors amenable to reduction by borane may beused with these polymers. In an alternative embodiment, for example, anyother borohydride such as ammonium borohydride, calcium borohydride, orothers may be produced instead of sodium borohydride by using variousrespective carbonate salts as a complimentary precursor reagent.

Other combinations of precursors known in the art to form borohydridescan also be used with this invention.

Example 2 In Situ Production of Methanol Fuel Mixtures

Another aspect of the present invention allows for in situ formation ofmethanol. Methanol is usable in many types of fuel cells, e.g., DMFC,enzyme fuel cell, reformat fuel cell, among others. As mentioned above,direct methanol fuel cells react according to the following chemicalformula:CH₃OH+1.5O₂→CO₂+2H₂O

To produce methanol, dimethyl dicarbonate and water are used asprecursor reagents. Also known as dimethylpyrocarbonate, dimethyldicarbonate (“DMDC”) is marketed by Bayer AG under the trade nameVELCORIN®. DMDC breaks down rapidly in aqueous environments. DMDC istaught as a cold sterilant in U.S. Pat. Nos. 6,563,207 and 5,866,182 andUnited States published patent application no. 2002/0012737, all ofwhich are incorporated herein by reference in their entireties.

When reacted with water at ambient temperatures, DMDC breaks down intomethanol and carbon dioxide. Thus, the ambient decomposition of DMDC((CH₃OCO)₂O) into methanol occurs according to the following chemicalequation:(CH₃OCO)₂O+H₂O→2CH₃OH+2CO₂

Because this process occurs at room temperature, the formation ofmethanol can be achieved for use in various fuel supplies forelectronics devices that operate at room temperature. Unlike methanol,moreover, DMDC is less corrosive. For instance, because it is lesscorrosive than methanol it can be less harmful to containment materials,such as seals, o-rings and overall packaging materials, especiallyduring long periods of storage prior to its use as a precursor to fuelfor a fuel cell. As such, DMDC is well-suited for use as a chemicalprecursor reagent for fuel cells that use methanol and water as fuel.For example, when combined with a molar excess amount of water, DMDCwill produce methanol and carbon dioxide (which can be vented or used topressurize the cartridge as needed) leaving the excess water to reactwith methanol as part of an overall fuel cell reaction, e.g., DMFC.Alternatively, other precursors amenable to the formation of methanolmay be used in this aspect of the invention.

Moreover, in situ production of methanol can be accomplished using anyfuel supply, including but not limited to, the embodiments describedabove.

Other examples of fuel cell fuels that can be stored in the fuel supplyas precursor reagents include, but are not limited to, ammonia boraneand hydrazine. These fuels can be reformatted into hydrogen. Ammoniaborane can be reformatted at temperatures of 100° C. and above, andhydrazine can be reformatted at room temperature, but itself requirestemperatures of 100° C. and above for its creation. They can both beused in power generation and automotive applications among others.

Ammonia borane reacts as follows to form hydrogen:NH₃BH₃+H₂O+heat→NH₂BH_(2(solid))+H₂This reaction is fully described in “Analysis of Hydrogen ProductionUsing Ammonia and Ammonia-Borane Complex for Fuel Cell Applications,”Hydrogen, Fuel Cells, and Infrastructure Technologies, FY 2002 ProgressReport, Ali T-Raissi, athttp://www.eere.energy.gov/hydrogenandfuelcells/pdfs/33098_sec5.pdf, andin “Portable Hydrogen Generator,” The Alchemist, 30 Sep. 2003, TinaWalton, available athttp://www.chemweb.com/alchem/articles/1063811899357.html. Thesereferences are incorporated herein by reference in their entireties.Ammonia borane can be produced from the following reaction:2NH_(3(aq))+B₂H_(6(aq))→2NH₃BH_(3(aq))Hence, ammonia and diborane are the precursor reagents that can react inwater to form ammonia borane fuel. As discussed in Example 1, severalborane-containing polymers disclosed in the '293 patent can besubstituted for diborane.

Hydrazine is soluble in water and decomposes to form hydrogen asfollows:N₂H₄H₂O+H₂O→2H₂+N₂+2H₂OHydrazine can be produced from methylethylazine hydrolysed at hightemperature, as follows:(CH₃C₂H₅CN)₂+3H₂O+heat→N₂H₄H₂O+2CH₃C₂H₅COMethylethylazine is formed from hydrogen peroxide, ammonia, and methylethyl ketone (MEK) at room temperature, as follows:H₂O₂+2NH₃+2CH₃C₂H₅CO→(CH₃C₂H₅CN)₂+4H₂OHence, hydrogen peroxide, ammonia and MEK can be stored as precursorreagents to hydrazine. The reaction to produce hydrazine is described inU.S. Pat. No. 6,517,798, which is incorporated herein by reference inits entirety.

All of the above Examples have various alternative embodimentsencompassed by the present invention.

While it is apparent that the illustrative embodiments of the inventiondisclosed herein fulfill the objectives of the present invention, it isappreciated that numerous modifications and other embodiments may bedevised by those skilled in the art. Additionally, feature(s) and/orelement(s) from any embodiment may be used singly or in combination withother embodiment(s). Therefore, it will be understood that the appendedclaims are intended to cover all such modifications and embodiments thatwould come within the spirit and scope of the present invention.

We claim:
 1. A method for making a fuel for a fuel cell, comprising:storing a first precursor reagent and a second precursor reagent withina portable fuel supply; isolating the first precursor reagent from thesecond precursor reagent within the portable fuel supply; and causingthe first precursor reagent to come into contact with the secondprecursor reagent to react to form the fuel within the portable fuelsupply; wherein the fuel created contains substantially no freehydrogen, and wherein the fuel remains with unreacted precursors.
 2. Themethod of claim 1, wherein the reaction between the two precursor agentsoccurs inside the fuel supply.
 3. The method of claim 1, wherein thereaction between the two precursor agents occurs at ambient temperature.4. The method of claim 1, wherein the first precursor reagent isdimethyl dicarbonate and the second precursor is water and the reagentsreact to form methanol.
 5. The method of claim 1, wherein the firstprecursor reagent is a carbonate and the second precursor reagent isborane or diborane and the reagents react to form a borohydride.
 6. Themethod of claim 5, wherein the carbonate is sodium carbonate and thefuel is sodium borohydride.
 7. The method of claim 5, wherein the boraneis stored as borane polymers.
 8. The method of claim 1, wherein thefirst precursor reagent is ammonia and the second precursor reagent isborane or diborane and the reagents react to form ammonia borane.
 9. Themethod of claim 8, wherein the borane is stored as borane polymers. 10.The method of claim 1, wherein the first precursor reagent ismethylethylazine and the second precursor reagent is water and thereagents react at elevated temperature to form hydrazine.
 11. The methodof claim 10, wherein the first precursor reagent methylethylazine isformed by reacting hydrogen peroxide, ammonia and methyl ethyl ketone,and wherein the hydrogen peroxide, ammonia and methyl ethyl ketone arestorable as precursor reagents.